In inkjet printing, the underlying principle is to convert a pulse of electric energy into a mechanical pressure pulse sufficient to overcome surface tension forces, holding fluid at a nozzle of a very small volume chamber. Generally, two technologies, piezoelectric and thermal actuators, have been utilized in inkjet printing.
One example of piezoelectric actuation of inkjet printheads is disclosed in U.S. Pat. No. 5,604,522, entitled “INK JET HEAD AND A METHOD OF MANUFACTURING THE INK JET HEAD”, the entire disclosure of which is incorporated herein by reference, as if being set forth in its entirety. Therein is disclosed an ink jet head for forcibly discharging ink droplets through nozzle openings in a manner that a pressure of ink within an ink chamber is increased by displacing a vibrating plate constituting a part of the ink chamber by a piezoelectric transducer. The vibrating plate is formed of a high polymeric resin thin film and rigid protrusions resin directly fastened to the high polymeric resin thin film. With such a construction, an expanding/contracting motion of the piezoelectric transducer is transferred to the ink chamber, enlarging a minute contact area of the piezoelectric transducer and amplifying the pushing force to the ink chamber. However, it may be desirable to exert higher pressures on ink chambers than may conventionally be achievable using piezoelectric actuators. Further, disadvantages of piezoelectric based printing may also include the cost of manufacturing piezo materials, since the volume displacement of the ink is based on the shear deflection of piezo itself, and this displacement is limited by the size of the piezo.
In a thermally actuated inkjet printhead, a resistor is conventionally pulsed to heat an adjacent sheath of ink within the ink chamber. Boiling is forced to occur, typically within a few microseconds, by heating a film of water-based fluid to ˜300° C., or nearly three times its normal boiling temperature. While this may result in an actuator that is many times smaller than typical piezoelectric transducer for the same job (i.e., for the same drop volume and velocity), it may impart an undesirable temperature fluctuation to the ink for example. A disadvantage of a thermal inkjet actuator may be its limited number of cycles though, as the number of working cycle times of thermal inkjet may be significantly less than that of a piezoelectric actuator.